What transition in the hydrogen spectrum would have the same wavelength as the Balmer transition `n = 4 to n = 2 of He^(+)`  spectrum?

Answer

A, B

Explanation

For `He^(o+), (1)/(lambda) = R_(H) xx (2)^(2) [(1)/((2)^(2))- (1)/((4)^(2))]`This may be simplified to the form
`(1)/(lambda) = R_(H) = [((2)^(2))/((2)^(2))- ((2)^(2))/((4)^(2))] = R_(H)[(1)/((1)^(2))- (1)/((2)^(2))]`
Thus for hydrogen atom `n = 2` to `n = 1 ` , transition would given radiation of teh same wavelength as `n = 4 "to" n = 2` transition for `He^(o+)`